A typical photographic element contains multiple layers of light-sensitive photographic silver halide emulsions with one or more of these layers being spectrally sensitized to blue light, green light, or red light. The blue, green, and red light sensitive layers will typically contain yellow, magenta or cyan dye forming couplers, respectively.
For forming color photographic images, the color photographic material is exposed imagewise and processed in a color developer bath containing an aromatic primary amine color developing agent. Image dyes are formed by the coupling reaction of these couplers with the oxidized product of the color developing agent. Generally, image couplers are selected to provide image dyes with good stability towards heat and light and which desirably have low unwanted side absorptions in order to provide color photographic images with good color reproduction.
The couplers used to produce cyan image dyes are generally derived from phenols and naphthols, as described, for example, in U.S. Pat. Nos. 2,367,351, 2,423,730, 2,474,293, 2,772,161, 2,772,162, 2,895,826, 2,920,961, 3,002,836, 3,466,622, 3,476,563, 3,880,661, 3,996,253, 3,758,308, in French patents 1,478,188 and 1,479,043, and in British patent 2,070,000. These types of couplers can be used either by being incorporated in the photographic silver halide emulsion layers or externally in the processing baths. In the former case the couplers must have ballast substituents built into the molecule to prevent the couplers from migrating from one layer into another. Although these couplers have been used extensively in photographic film and paper products, the dyes derived from them still suffer from undesirable side absorptions, causing considerable reduction in color reproduction.
Cyan couplers which have been so far proposed to overcome this problem are nitrogen containing heterocyclic couplers as disclosed in U.S. Pat. Nos. 4,728,598, 4,818,672, 4,873,183, 4,916,051, 5,118,812, 5,206,129, and EP patent 249,453A. Even though cyan dyes produced by these couplers show a reduction in their undesirable side absorptions, these couplers exhibit undesirably low coupling activity. Furthermore, the dyes derived from them have very low stability against heat, light, and have a very short absorption peak (.lambda.-max). These disclosed novel couplers are therefore not practical for use in photographic products.
Other cyan couplers proposed for improving color reproduction are disclosed in U.S. Pat. Nos. 3,552,962, 3,839,044, 4,960,685, and German patent publications DE 3,005,355 and 3,022,915. All these couplers are based on a well known coupler parent disclosed in U.S. Pat. No. 3,002,836 that is currently used in photographic color film products (see formula I). However, to use these couplers as incorporated couplers in the silver halide emulsion layers, and to achieve the same sharp-cutting dye hue as provided by coupler represented by formula (I), these couplers must by necessity be ballasted in the aryloxy coupling-off groups or be anchored to a suitable polymeric backbone as illustrated by formula (II). ##STR2##
While these latter couplers will form the same dye as those provided by formula (I), their color reproducibility is highly variable and highly dependent on the type and nature of the coupling-off groups, which, because of the ballasts, are not readily washed out of the photographic layers during processing.
In addition to the forgoing, many naphtholic couplers have been notorious for their susceptibility to leuco dye formation in the presence of ferrous ion. Ferrous ion is generated in the bleach or bleach/fix bath as a result of the reduction of ferric ion during the bleaching process. The ferrous ion may than react with the naphtholic dye to eliminate the nitrogen double bond rendering the dye colorless. This manifests itself as a loss in dye density.
It is a problem to be solved to provide a photographic element containing a cyan coupled which exhibits excellent photographic properties such as reduced side absorptions of the formed dye, particularly on the short wavelength side of the spectrum, and improved stability towards ferrous ion reduction in the processing bleach or bleach-fix bath.